1. Field of the Invention
The present invention relates to a flow sensor device to obtain flow characteristics of a fluid flow system, such as a system used in administering a beneficial agent to a patient. Particularly, the present invention is directed to a flow measurement device including first and second pressure sensors in a flow passage to measure a flow of beneficial agent and, optionally, the presence of air in the fluid flow system. The invention also includes a related system and method for obtaining such flow characteristics.
2. Description of Related Art
When administering a predetermined amount of a beneficial agent to a patient over an extended period of time in liquid form, it is beneficial, if not necessary, to obtain and monitor relevant flow characteristics such as flow rates and the presence of air. While methods for obtaining such information have existed for a long time, to date, no reliable low cost systems have been developed for disposable use.
For example, fluid flow measurements within a disposable IV fluid line or similar feed set generally have not been financially and technically viable up to this point in time. Low cost electronic flow sensors have existed for some time, but have to date not presented a viable alternative for solving this problem. Limitations to commercialization of such a device have included inadequate dynamic range of low-cost flow sensor systems and the unacceptable costs of total sensor assembly.
One problem with making flow sensors low cost is in the manufacturing process. Silicon chips typically are wire-bonded to a lead frame that is encapsulated and soldered to a printed circuit board. This configuration requires the manual step of welding wires from the chip to the lead frame, which can result in significant additional manufacturing costs.
Likewise, there has been a long-felt need in the medical field for an economical and reliable system to detect the presence of air in IV lines or other medical feed sets. Typically, the presence of air in a fluid line has been sensed externally to the fluid path using a separate ultrasound or optical sensor that must communicate through the disposable tubing or molded component of the fluid path. The ultrasound approach may be subject to misalignment and other geometry changes that can impact the signal conduction around and through the fluid inside the tubing or other components of the disposable fluid path. The optical approach requires specific molded geometries within the fluid path that are reflective or conductive depending on the presence of air or liquid. These systems are subject to variability in and interfacing to the disposable fluid path. Also, the added cost of this air detection system is an impediment to its widespread adoption.
Thus, there remains a need in the art for a reliable fluid flow detection system that is sufficiently inexpensive to allow use in disposable applications. There is also a continued need for an inexpensive and reliable system to detect the presence of air in fluid systems, such as IV lines and feed sets.
The purpose and advantages of the present invention will be set forth in and apparent from the description that follows, as well as will be learned by practice of the invention. Additional advantages of the invention will be realized and attained by the methods and systems particularly pointed out in the written description and claims hereof, as well as from the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described, the invention is directed to a device for obtaining flow characteristics of a fluid flow system.
The device includes a sensor assembly. The sensor assembly includes a body defining a first fluid flow passage having an inlet and an outlet, and a flow restricting element located along the first fluid flow passage between the inlet and the outlet. An upstream fluid pressure sensor is provided to sense an upstream fluid pressure at an upstream location in the first fluid flow passage between the inlet and the flow restricting element. The sensor assembly also includes a downstream fluid pressure sensor to sense a downstream fluid pressure at a downstream location in the first fluid flow passage between the flow restricting element and the outlet. The sensor assembly also includes an upstream signal contact connected to the upstream fluid pressure sensor, and a downstream signal contact connected to the downstream fluid pressure sensor.
The device also includes a housing. The housing has an upstream portion and a downstream portion. The upstream portion of the housing defines an upstream port in fluid communication with the inlet of the sensor assembly. The downstream portion of the housing defines a downstream port in fluid communication with the outlet of the sensor assembly. The housing also defines a probe access port configured to provide access of a probe to at least one of the upstream signal contact and downstream signal contact.
In accordance with another aspect of the invention, the housing has at least one registration surface configured to ensure proper registration of the device with a fluid flow system. The registration surface ensures the upstream port is aligned with a fluid source. The registration surface can include a surface configuration on the upstream portion of the housing that is different from a surface configuration on the downstream portion of the housing. In accordance with one aspect of the invention, the registration surface includes at least one planar surface. The registration surface can also include a detent.
In accordance with a further aspect of the invention, the housing defines a cavity of predetermined shape, and the sensor assembly has a corresponding shape so as to be received by the cavity. The cavity has at least one surface, and the surface can include at least one recess to receive a material to hold the sensor assembly within the cavity. A cap can further be positioned in the cavity proximate to the sensor assembly. The housing can have a connector, such as a Luer connector or a flange, proximate to at least one of the upstream port and the downstream port for connection with the fluid flow system.
In accordance with another aspect of the invention, the housing can define a second fluid flow passage therethrough. The second fluid flow passage can be arranged for fluid communication in parallel with the first fluid flow passage between the upstream port and the downstream port. A valve can further be provided for selective flow through the second fluid flow passage. For example, the valve can be formed as a compressible wall member defining at least a portion of the second fluid flow passage. The compressible wall member can be formed from an elastomeric material. In a preferred embodiment, the second fluid flow passage has a first transverse dimension and a second transverse dimension perpendicular to the first transverse dimension. Preferably, the first dimension is smaller than the second dimension so as to be more readily compressible. Preferably, the cross section of the second fluid flow passage has an ellipsoidal shape with a small radius at each apex of the ellipse to facilitate compression of the second fluid flow passage.
In accordance with another aspect of the invention, a fluid sensor system is provided. The system includes a device for obtaining flow rate measurements as described above, as well as a probe to receive signals representative of a fluid flow characteristic and a processor to process such signals. The probe can include a connector body having a predetermined shape, such as a wedge configuration, wherein the probe access port has a corresponding shape to ensure proper alignment of the probe with at least one of the upstream signal contact and downstream signal contact. The probe also includes a plurality of leads. At least one lead is provided for communication with the upstream signal contact and at least one lead is provided for communication with the downstream signal contact. At least one lead on the probe is configured to wipe across at least one of the upstream signal contact and the downstream signal contact. Preferably, the housing is configured to provide contact on one longitudinal surface and one vertical surface of the housing and provide for adequate force to ensure contact between the lead on the probe and the upstream signal contact and the downstream signal contact. The signal contacts can be in close proximity to registration surfaces on the outside of the housing that are engaged with an external clamp assembly that is also referenced to the probe.
In accordance with a further aspect of the invention, the system further includes a fluid flow line in communication with a fluid source. A locking mechanism preferably is provided to mate the housing with the fluid flow line. The locking mechanism has an unlocked condition for receipt of the housing, a first locked condition to align the housing with the fluid flow line and a second locked condition to position the probe in the housing. Additionally, if a second fluid flow passage with a valve is defined in the housing as described above, the system can further include an actuator to change the valve from the first condition to the second condition when the locking mechanism is moved from the first locked condition to the second locked condition. The actuator can include a protrusion to compress the elastic wall member. In one embodiment of the invention, the protrusion is a pin.
In further accordance with the invention, the fluid source includes a pump connected to the fluid flow system to selectively pump fluid through the first fluid flow passage. The processor is configured to control the pump in response to signals obtained by the probe from the sensors.
In further accordance with the invention a method of obtaining flow measurements is provided. The method includes providing a device for obtaining flow rate measurements as described above; directing a fluid flow through the first fluid flow passage; obtaining a signal corresponding to the fluid pressure in the first fluid flow passage at the locations of the upstream fluid pressure sensor and the downstream fluid pressure sensor; and determining a flow characteristic based upon the signal.
In accordance with a further aspect of the invention, the determining step includes determining the pressure difference between the upstream and downstream fluid pressure sensors. The determining step can further include calculating a flow rate of fluid through the first fluid flow passage based on the pressure difference.
In accordance with another aspect of the invention, the determining step includes detecting the presence of air in the first fluid flow passage. The step of detecting air in the first fluid flow passage can include identifying convergence and specific waveforms of the signal received from the upstream fluid pressure sensor and the signal received from the downstream fluid pressure sensor.
In accordance with yet another aspect of the invention, a method is provided further including the steps of intermittently pulsing the fluid through the first fluid flow passage and determining the amount of fluid delivered with each pulse by detecting the fluid pressure in the first fluid flow passage using the upstream fluid pressure sensor and the downstream fluid pressure sensor.
In accordance with still another aspect of the invention, a method is provided wherein the housing provided by the housing step includes a second fluid flow passage and a valve for selection of flow through the second fluid flow passage. The valve has a first condition to allow flow through the second flow passage and a second condition to prevent flow through the second flow passage. The method further includes the step of opening the valve to increase flow through the housing.